Re: Ki, Aiki, Aikido. The 'internal stuff' that never left Aikido
George S. Ledyard
One should not only be able to keep it unbendable under pressure from a partner but bend it and straighten it without them being able to stop you. This should be done without tensing the arm muscles at all. If one has this type of energized flexibility, one has what is needed to execute technique without either clashing or collapsing which is what many folks do.
I agree but not with the tensing part seeing as some muscles do actually have to flex in order for the arm to move. Koretoshi Maruyama Sensei teaches that you should consider what your triceps are doing in all of this. Makes sense really as if you rely on your biceps you'll be bending your own arm for them. In any case doing this exercise correctly should mean that your arm is free to move and extend as and when you like it. But not when the tester does (unless they are better at this stuff than you are in which case things start getting..... interesting).